The Elements of Evolution (51-1-2) Bats

 Bat Echolocation

Echolocation is a dynamic system that allows different species, regardless of their body size, to converge on optimal fields of view in response to habitat and task. All bats adapted their calls to achieve similar acoustic fields of view. ~ Danish zoologist Lasse Jakobsen et al

Bats adjust their echolocation calls to go from surveying an area to pinpointing objects as they close in. How a bat does this depends upon its size, and especially depends upon its echolocation emitter: the mouth.

There is a strong relationship between bat body size and echolocation peak frequency, which is the maximum energy in echolocation calls. While large bats can produce focused beams at lower frequencies, smaller bats employ higher frequencies to achieve directional sonar beams.

The size of bat’s mouth determines its wavelength capabilities. Different bat species of equivalent size use sonar beams with selfsame beam shape and volume. This example of convergent evolution illustrates the functional nature of allometry.

 Bat Shelter and Sociality

22 species of bat are known to make tents for shelter. Most build their tents from palm leaves and other sturdy plant parts. These structures often last for more than a year.

Other tent makers cannot access such durable materials available. They rely upon herbaceous plants, which make rather ramshackle rooms that last for less than 2 months.

Domestic comfort does not make for social cohesion; quite the contrary. Nomadic bats that must make a new home every few weeks are much more collaborative.

In contrast, group cohesion in those species with sturdy shelters is low. Whereas frequent builder bats stick together for more than a year, no species that stays in long-lasting lodgings does.

As the cohesive bat species are not closely related, the social stability that went with frequent shelter building evolved independently. Adversity promotes solidarity.